DESCRIPTION: This proposal continues to use genetic, biochemical and molecular biological approaches to study the fundamental genetics, biology, and pathogenesis of the rotaviruses; a group of viruses that are the major cause of gastroenteritis in children and the young of other species. The studies focus on three broad areas: [i] fundamental genetics of the rotaviruses, [ii] studies relating to virus structure including visualization of protein interactions in reconstructions of virus particles and studies to identify specific domains of viral proteins that interact in virus particles, and [iii] studies of pathogenesis with special emphasis on infection at peripheral sites. The results of these studies will enhance the understanding of mechanisms of interaction between enteric viruses and the host, may reveal unique pathways characteristic of rotavirus infection, and will provide information potentially useful in development of vaccine control strategies and antiviral drugs. Three specific aims are proposed: (1) Genetic analysis of rotaviruses. Mutants will be mapped by complementation of unmapped ts mutant groups in cells expressing wild type proteins, mutations in structural genes will be fine-mapped by sequencing, and the biochemistry of infection with the mutants will be characterized. (2) Studies on assembly and morphology of infectious virus particles. Cryoelectron microscopy and computer-assisted reconstructions will be used to understand structural changes associated with activation of viral infectivity by protease cleavage of VP4, structural changes in reassortants with altered interactions among structural proteins, and to visualize actively replicating template RNA in replicase particles. Domains of structural proteins that interact in the virion will be further characterized by a combination of genetic, biochemical, and functional assays. (3) Studies of rotavirus pathogenesis and virulence. Studies will be continued to examine rotavirus infection of the liver including, identification of the block to replication of some virus strains in liver cells, identification of genes governing escape of virus from the gut to infect peripheral sites, and identify mutant genes and specific mutations in viruses adapted to grow in liver cells.